Medical devices, such as implantable cardioverter-defibrillators, provide therapeutic electrical stimulation to the heart in order to terminate tachyarrhythmia, such as tachycardia or fibrillation. The electrical stimulation may include signals such as pulses or shocks for pacing, cardioversion or defibrillation. In some cases, the medical device may sense intrinsic depolarizations of the heart, detect tachyarrhythmia based on the intrinsic depolarizations, and control delivery of electrical stimulation to the heart if tachyarrhythmia is detected based on the intrinsic depolarizations.
Medical devices sense cardiac electrical signals and deliver therapeutic stimulation via electrodes. Implantable pacemakers, cardioverters, defibrillators, or pacemaker-cardioverter-defibrillators are typically coupled to one or more intracardiac leads that carry electrodes for cardiac sensing and delivery of therapeutic stimulation. The cardiac electrical signals sensed via the electrodes may be referred to as a cardiac electrogram (EGM). In some systems, electrodes positioned outside the heart, for example in subcutaneous or submuscular locations are used to sense electrocardiogram (ECG) signals. The cardiac electrical signals include depolarizations and other intrinsic electrical activity of the heart.
In some cases, a medical device delivers therapeutic electrical stimulation, such as a defibrillation pulse, when the stimulation is not required. Delivery of such therapy by a medical device is often due to misinterpretation of the cardiac EGM (or ECG) as indicating a rapid or unstable ventricular tachycardia or ventricular fibrillation. In some cases, the medical device detects a rapid ventricular tachycardia or ventricular fibrillation when the cardiac rhythm is in fact stable, or otherwise not requiring a defibrillation pulse, such as sinus tachycardia (ST), supraventricular tachycardia (SVT), or rapid atrial tachycardia/atrial fibrillation (AT)/(AF) conducted to the ventricles, or a hemodynamically stable ventricular tachycardia (VT). In some cases, the medical device misinterprets T-waves in the cardiac EGM as R-waves, which is referred to as T-wave over-sensing (TWOS), and may cause the medical device to interpret the cardiac rhythm as having a higher ventricular rate than the actual rate. In some cases, the medical device over-senses R-waves due to non-physiological or non-cardiac signals in the cardiac EGM, which may be the result of electromagnetic interference (EMI), EGM clipping, lead fracture, or muscle noise, as examples. Implantable medical devices that detect the cardiac EGM via implantable medical leads may be susceptible to oversensing due to non-physiological or non-cardiac signals in the cardiac EGM.